Sheaths used with polymer scaffolds

ABSTRACT

A medical device includes a polymer scaffold crimped to a catheter having an expansion balloon. A sheath pair is placed over the crimped scaffold after crimping to reduce recoil of the crimped polymer scaffold and maintain scaffold-balloon engagement relied on to hold the scaffold to the balloon when the scaffold is being delivered to a target in a body. The sheath pair is removed by a health professional before placing the scaffold within the body.

FIELD OF THE INVENTION

The present invention relates to drug-eluting medical devices; moreparticularly, the invention relates to sheaths for polymeric scaffoldscrimped to a delivery balloon.

BACKGROUND OF THE INVENTION

A variety of non-surgical interventional procedures have been developedover the years for opening stenosed or occluded blood vessels in apatient caused by the build up of plaque or other substances on thewalls of the blood vessel. Such procedures usually involve thepercutaneous introduction of an interventional device into the lumen ofthe artery. In one procedure the stenosis can be treated by placing anexpandable interventional device such as an expandable stent into thestenosed region to hold open and sometimes expand the segment of bloodvessel or other arterial lumen. Metal or metal alloy stents have beenfound useful in the treatment or repair of blood vessels after astenosis has been compressed by percutaneous transluminal coronaryangioplasty (PTCA), percutaneous transluminal angioplasty (PTA) orremoval by other means. Metal stents are typically delivered in acompressed condition to the target site, then deployed at the targetinto an expanded condition or deployed state to support the vessel.

The following terminology is used. When reference is made to a “stent”,this term will refer to a metal or metal alloy structure, generallyspeaking, while a scaffold will refer to a polymer structure. It isunderstood, however, that the art sometimes uses the term “stent” whenreferring to either a metal or polymer structure.

Metal stents have traditionally fallen into two generalcategories—balloon expanded and self-expanding. The later type expandsto a deployed or expanded state within a vessel when a radial restraintis removed, while the former relies on an externally-applied force toconfigure it from a crimped or stowed state to the deployed or expandedstate.

Self-expanding stents formed from, for example, shape memory metals orsuper-elastic alloys such as nickel-titanum (NiTi) which are designed toautomatically expand from a compressed state when the radial restraintis withdrawn or removed at the distal end of a delivery catheter intothe body lumen, i.e. when the radial restraint is withdrawn or removed.Typically, these stents are delivered within a radially restrainingpolymer sheath. The sheath maintains the low profile needed to navigatethe stent towards the target site. Once at the target site, the sheathis then removed or withdrawn in a controlled manner to facilitatedeployment or placement at the desired site. Examples of self-expandingstents constrained within a sheath when delivered to a target sitewithin a body are found in U.S. Pat. No. 6,254,609, US 20030004561 andUS 20020052640.

Balloon expanded stents, as the name implies, are expanded uponapplication of an external force through inflation of a balloon, uponwhich the stent is crimped. The expanding balloon applies a radialoutward force on the luminal surfaces of the stent. During the expansionfrom a crimped or stowed, to deployed or expanded state the stentundergoes a plastic or irreversible deformation in the sense that thestent will essentially maintain its deformed, deployed state afterballoon pressure is withdrawn.

Balloon expanded stents may also be stored within a sheath, eitherduring a transluminal delivery to a target site or during the assemblyor in the packaging of the stent-balloon catheter delivery system. Theballoon expanded stent may be contained within a sheath when deliveredto a target site to minimize dislodgment of the stent from the balloonwhile en route to the target vessel. Sheaths may also be used to protecta drug eluting stent during a crimping process, which presses or crimpsthe stent to the balloon catheter. When an iris-type crimping mechanism,for example, is used to crimp a stent to balloon, the blades of thecrimper, often hardened metal, can form gouges in a drug-polymer coatingor even strip off coating through interaction similar to forces at playwhen the blades and/or stent struts are misaligned during the diameterreduction. Examples of stents that utilize a sheath to protect the stentduring a crimping process are found in U.S. Pat. No. 6,783,542 and U.S.Pat. No. 6,805,703.

A polymer scaffold, such as that described in US 20100004735 may be madefrom a biodegradable, bioabsorbable, bioresorbable, or bioerodablepolymer. The terms biodegradable, bioabsorbable, bioresorbable,biosoluble or bioerodable refer to the property of a material or stentto degrade, absorb, resorb, or erode away after the scaffold has beenimplanted at the target vessel. The polymer scaffold described in US2010/0004735, as opposed to a metal stent, is intended to remain in thebody for only a limited period of time. In many treatment applications,the presence of a stent in a body may be necessary for a limited periodof time until its intended function of, for example, maintainingvascular patency and/or drug delivery is accomplished. Moreover, it isbelieved that biodegradable scaffolds, as opposed to a metal stent,allow for improved healing of the anatomical lumen and reduced incidenceof late stent thrombosis. For these reasons, there is a desire to treata vessel using a polymer scaffold, in particular a bioerodible polymerscaffold, as opposed to a metal stent, so that the prosthesis's presencein the vessel is for a limited duration. However, there are numerouschallenges to overcome when developing a delivery system having apolymer scaffold.

Polymer material considered for use as a polymeric scaffold, e.g.poly(L-lactide) (“PLLA”), poly(L-lactide-co-glycolide) (“PLGA”),poly(D-lactide-co-glycolide) or poly(L-lactide-co-D-lactide)(“PLLA-co-PDLA”) with less than 10% D-lactide, and PLLD/PDLA stereocomplex, may be described, through comparison with a metallic materialused to form a stent, in some of the following ways. A suitable polymerhas a low strength to weight ratio, which means more material is neededto provide an equivalent mechanical property to that of a metal.Therefore, struts must be made thicker and wider to have the requiredstrength for a stent to support lumen walls at a desired radius. Thescaffold made from such polymers also tends to be brittle or havelimited fracture toughness. The anisotropic and rate-dependant inelasticproperties (i.e., strength/stiffness of the material varies dependingupon the rate at which the material is deformed) inherent in thematerial only compound this complexity in working with a polymer,particularly, bio-absorbable polymer such as PLLA or PLGA. Challengesfaced when securing a polymer scaffold to a delivery balloon arediscussed in U.S. patent application Ser. No. 12/861,719 (Attorneydocket 62571.448).

When using a polymer scaffold, several of the accepted processes formetal stent handling can no longer be used. A metal stent may be crimpedto a balloon in such a manner as to minimize, if not eliminate recoil inthe metal structure after removal from the crimp head. Metal materialsused for stents are generally capable of being worked more during thecrimping process than polymer materials. This desirable property of themetal allows for less concern over the metal stent-balloon engagementchanging over time when the stent-catheter is packaged and awaiting usein a medical procedure. Due to the material's ability to be workedduring the crimping process, e.g., successively crimped and released athigh temperatures within the crimp mechanism, any propensity for elasticrecoil in the material following crimping can be significantly reduced,if not eliminated, without affecting the stent's radial strength whenlater expanded by the balloon. As such, following a crimping process thestent-catheter assembly often does not need packaging or treatment tomaintain the desired stent-balloon engagement and delivery profile. Ifthe stent were to recoil to a larger diameter, meaning elasticallyexpand to a larger diameter after the crimping forces are withdrawn,then significant dislodgment force could be lost and the stent-balloonprofile not maintained at the desired diameter needed to deliver thestent to the target site.

While a polymer scaffold may be formed so that it is capable of beingcrimped in such a manner as to reduce inherent elastic recoil tendenciesin the material when crimped, e.g., by maintaining crimping blades onthe scaffold surface for an appreciable dwell period, the effectivenessof these methods are limited. Significantly, the material generally isincapable of being worked to the degree that a metal stent may be workedwithout introducing deployed strength problems, such as excessivecracking in the material. Recoil of the crimped structure, therefore, isa problem that needs to be addressed.

In view of the foregoing, there is a need to address the challengesassociated with securing a polymer scaffold to a delivery balloon andmaintaining the integrity of a scaffold-balloon catheter delivery systemup until the time when the scaffold and balloon are delivered to atarget site within a body.

SUMMARY OF THE INVENTION

The invention is directed to sheaths used to maintain polymer scaffoldballoon engagement and delivery system profile as well as methods forassembly of a medical device including a balloon expandable polymerscaffold contained within a sheath. The invention is also directed to asheath and methods for applying a sheath that enable the sheath to beeasily removed by a medical professional, e.g., a doctor, in anintuitive manner without disrupting the crimped scaffold-balloonengagement or damaging the scaffold. Sheaths according to the inventionare removed before the medical device is introduced into a patient.

Sheaths according to the invention are particularly useful formaintaining scaffold-balloon engagement and desired delivery profilefollowing a crimping process for scaffolds formed at diameters largerthan the delivered diameter are crimped down to achieve a smallercrossing-profile, or crimped diameter. A scaffold formed at a largerdiameter, near to or greater than the intended deployed diameter, canexhibit enhanced radial strength when supporting a vessel, as comparedto a scaffold formed nearer to a crimped diameter. A scaffold formednear to a deployed diameter, however, increases the propensity forelastic recoil in the scaffold following the crimping process, due tothe shape memory in the material. The shape memory relied on forenhancing radial strength at deployment, therefore, also introducesgreater elastic recoil tendencies for the crimped scaffold. Recoil bothincreases the crossing profile and reduces the scaffold-balloonengagement needed to hold the scaffold on the balloon. In one aspect,the invention is directed to maintaining the crossing profile and/ormaintaining balloon-scaffold engagement for scaffolds formed near to adeployed diameter.

In another aspect, the invention is directed to a method of assembly ofa catheter that includes crimping a polymer scaffold to a balloon of thecatheter and within a short period of removal of the scaffold from thecrimper placing a restraining sheath over the scaffold. The steps mayfurther include applying an extended dwell time following a finalcrimping of the scaffold, followed by applying the restraining sheath.Both the crimping dwell time and applied restraining sheath are intendedto reduce recoil in the crimped scaffold. The restraining sheath mayinclude both a protecting sheath and a constraining sheath.

In another aspect, the invention is directed to a sterilized medicaldevice, e.g., by E-beam radiation, contained within a sterile package,the package containing a scaffold crimped to a balloon catheter and asheath disposed over the crimped scaffold to minimize recoil of thecrimped scaffold. The sheath covers the crimped scaffold and extendsbeyond the distal end of the catheter. The sheath may extend at leastthe length of the scaffold beyond the distal end of the catheter. At thedistal end of the sheath there is a portion configured for beingmanually grabbed and pulled distally of the catheter to remove thesheath from the catheter. In one embodiment, this portion is part of theprotecting sheath. In another embodiment, the portion is part of theconstraining sheath.

In another aspect, the invention is directed to an apparatus and methodsfor removing a sheath pair from a scaffold in a safe, intuitive mannerby a health professional. According to this aspect of the invention, thesheath pair may be removed by a medical specialist such as a doctorwithout risk of the scaffold becoming dislodged from the balloon ordamaged, such as when the sheath pair is accidentally removed in animproper manner by a health professional.

Sheaths arranged according to the invention provide an effective radialconstraint for preventing recoil in a crimped scaffold, yet arecomparatively easy to manually remove from the scaffold. A sheath thatapplies a radial constraint can be difficult to remove manually withoutdamaging the crimped scaffold, dislodging or shifting it on the balloon.In these cases it is desirable to arrange the sheaths in a manner toapply an effective radial constraint yet make the sheaths capable ofmanual removal in a safe and intuitive manner. By making the sheathremoval process easy to follow and intuitive, the possibility that ahealth professional will damage the medical device when removing thesheath is reduced.

According to another aspect of the invention a crimped scaffold isconstrained within a protecting sheath and a constraining sheath. Theprotecting sheath, or protecting portion, protects the integrity of thecrimped scaffold-balloon structure while the constraining sheath orconstraining portion, is applied and/or removed from the crimpedscaffold. Arranged in this manner a radial inward force may be appliedto a crimped scaffold via a sheath, without risking dislodgement orshifting of the scaffold on the balloon when the sheath is manuallyremoved.

According to another aspect, a sheath is formed to reduce frictionalresistance when being removed from the scaffold. The sheath may includea constraining sheath disposed over a protecting sheath, or the sheathmay be disposed directly over the scaffold. According to suchembodiments, the reduced frictional resistance can minimize harmfulshearing forces applied to the scaffold when the sheath is beingremoved.

According to another aspect of the invention, a sheath pair is used toimpose a higher radial inward constraint on a crimped polymer scaffoldthan is possible using a single sheath that must be manually removedfrom the scaffold before the scaffold can be introduced into a patient.

According to another aspect of the invention, there is provided either aone or two piece sheath for constraining a scaffold. In either case, thesheath may include both a constraining portion and protecting portion.

According to another aspect of the invention, a sheath pair covering acrimped scaffold is removed by sliding a first sheath over a connectedsecond sheath. After the first sheath has been displaced a sufficientdistance, a connector connecting the sheaths withdraws the secondsheath.

According to another aspect of the invention, a sheath includes aprotecting portion that closes around a scaffold when a compressionportion is inserted over the protecting portion. A handling portion,surrounding the compression portion, connected to the protectingportion, is included to remove the protecting portion from the scaffold,after the compression portion is removed.

According to another aspect of the invention, tabs are disposed betweena constraining sheath and the scaffold. To remove the constrainingsheath, the tabs are pulled radially outward to push the scaffold off ofa distal end of the catheter. According to one such embodiment, theconstraining sheath may be heat shrunk over the tabs and scaffold toprovide a radially inward constraining force on the scaffold.

In accordance with the foregoing objectives, in one aspect of theinvention there is a method for assembling a scaffold-balloon catheter,comprising providing a balloon-catheter having a scaffold crimped to theballoon; and constraining the crimped scaffold including placing thecrimped scaffold within a protecting portion, and then placing thescaffold and protecting portion within a constraining portion, whereinthe protecting portion and constraining portion are integral portions ofa sheath; wherein the scaffold is configured for being passed throughthe body of a patient only after the sheath is removed from the crimpedscaffold.

In another aspect, there is an apparatus, comprising a catheter assemblyhaving a distal end and including a scaffold comprising a polymercrimped to a balloon; a sheath disposed over the scaffold, the sheathapplying a radial inward force on the crimped scaffold to limit recoilof the scaffold, the sheath comprising a protecting portion having adistal end, a constraining portion disposed over the protecting portion,and a connector portion connecting the protecting portion andconstraining portion; wherein the apparatus is configured for beingpassed through the body of a patient only after the sheath is removed.

In another aspect, there is method for assembling a scaffold-ballooncatheter, comprising providing a balloon-catheter having a scaffoldcrimped to the balloon; and constraining the crimped scaffold using atwo-piece sheath, including placing the crimped scaffold within aprotecting portion of the sheath, then placing a constraining portion ofthe sheath over the protecting portion; wherein the scaffold isconfigured for being passed through the body of a patient only after theconstraining portion and protecting portion are removed from the crimpedscaffold.

In another aspect, there is an apparatus, comprising a catheter assemblyhaving a distal end and including a scaffold comprising a polymercrimped to a balloon; a two-piece sheath disposed over the scaffold, thesheath applying a radial inward force on the crimped scaffold to limitrecoil of the scaffold, the sheath comprising a protecting portion, anda constraining portion disposed over the protecting portion; wherein theapparatus is configured for being passed through the body of a patientonly after the two-piece sheath is removed.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in the presentspecification are herein incorporated by reference to the same extent asif each individual publication or patent application was specificallyand individually indicated to be incorporated by reference. To theextent there are any inconsistent usages of words and/or phrases betweenan incorporated publication or patent and the present specification,these words and/or phrases will have a meaning that is consistent withthe manner in which they are used in the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a polymer scaffold-balloon catheter assembly(medical device) with a pair of sheaths placed over the crimpedscaffold.

FIG. 1A shows a side view cross-section of a portion of the device ofFIG. 1 at a proximal end thereof.

FIG. 2A is a perspective view of the sheath pair of FIG. 1.

FIGS. 2B-2D show a side view, and first and perspective views of aprotecting sheath of the sheath pair of FIG. 2A.

FIGS. 3A-3D illustrate a method of securing the sheath pair of FIG. 2Ato a distal end of the catheter assembly of FIG. 1.

FIGS. 4A-4C illustrate a method of removing the sheath pair of FIG. 2Afrom the distal end of the catheter assembly of FIG. 1.

FIG. 5 is a side view of a polymer scaffold-balloon catheter assembly(medical device) with a pair of sheaths placed over the crimped scaffoldaccording to an alternative embodiment.

FIG. 6A illustrates a side view of the sheath pair of FIG. 5.

FIG. 6B illustrates a method of placing the sheath pair of FIG. 6A overthe scaffold-balloon catheter assembly to arrive at the assembled viewof FIG. 5.

FIG. 6C shows a portion of the proximal end of the assembled device ofFIG. 5 with a clamp used to secure the sheath pair of FIG. 5 in positionrelative to the scaffold-balloon catheter assembly according to analternative embodiment.

FIG. 6D shows the sheath pair of FIG. 6A when formed from a single pieceof tubing.

FIGS. 7A-7C show front and side views of a constraining sheath having aninner surface for reducing friction between the constraining sheath anda protecting sheath according to alternative embodiments.

FIGS. 8A-8B show front and side views of a constraining sheath having aninner surface for reducing friction between the constraining sheath anda protecting sheath according to another alternative embodiment.

FIGS. 9A-9B show front and side views of a constraining sheath having aninner surface for reducing friction between the constraining sheath anda protecting sheath according to other alternative embodiments.

FIGS. 10A-10D depicts perspective and front views of a sheath assemblyaccording to another embodiment.

FIGS. 11A-11C shows a polymer scaffold-balloon catheter assembly with apair of sheaths placed over the crimped scaffold, and removed from thescaffold according to another alternative embodiment.

FIGS. 12A-12B shows a polymer scaffold-balloon catheter assembly with asheath having an inner sleeve placed over the crimped scaffold, andremoved from the scaffold according to another alternative embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

A polymer scaffold according to a preferred embodiment is formed from aradially expanded or biaxially expanded extruded PLLA tube. The scaffoldis laser cut from the expanded tube. The diameter of the tube ispreferably selected to be about the same, or larger than the intendeddeployed diameter for the scaffold to provided desirable radial strengthcharacteristics, as explained earlier. The scaffold is then crimped ontothe balloon of the balloon catheter. Preferably, an iris-type crimper isused to crimp the scaffold to the balloon. The desired crimped profilefor the scaffold is ½ or less than ½ of the starting (pre crimp)diameter of the expanded tube and scaffold. In the embodiments the ratioof the starting diameter (before crimping) to the final crimp diametermay be 2:1, 2.5:1, 3:1, or higher. For example, the ratio of startingdiameter to final crimped diameter may be greater than the ratio of thedeployed diameter to the final crimped diameter of the scaffold, e.g.,from about 4:1 to 6:1.

The pre-crimp memory in the scaffold material following crimping willinduce some recoil when the scaffold is removed from the crimper. Whilea dwell period within the crimper can reduce this recoil tendency, it isfound that there is residual recoil that needs to be restrained whilethe scaffold is awaiting use. This is done by placing a restrainingsheath over the scaffold immediately after the crimper blades arereleased and the scaffold removed from the crimper head. This need toreduce recoil is particularly evident when the diameter reduction duringcrimping is high, since for a larger starting diameter compared to thecrimped diameter the crimped material can have higher recoil tendencies.Examples of polymers that may be used to construct sheaths describedherein are Pebax, PTFE, Polyethelene, Polycarbonate, Polyimide andNylon. Examples of restraining sheaths for polymer scaffold, and methodsfor attaching and removing restraining sheaths for polymer scaffold aredescribed in U.S. application Ser. No. 12/916,349 (docket no. 104584.7).

FIG. 1 shows a side view of a distal portion of a scaffold-ballooncatheter assembly 2. The catheter assembly 2 includes a catheter shaft 4and a scaffold 10 crimped to a delivery balloon 12. As shown there aretwo separate sheaths 20, 30 disposed over the scaffold 10. The scaffold10 is contained within a protecting sheath 20 and a constraining sheath30, which is slid over the outer surface of the protecting sheath 20 toposition it over the scaffold 10. Before inserting the catheter assembly2 distal end within a patient, both the constraining sheath 30 andprotecting sheath 20 are removed by a health professional.

The sheaths 20, 30 provide an effective radial constraint for reducingrecoil in the crimped scaffold 10. Yet the sheaths 20, 30 are alsoeasily removed by a health professional at the time of a medicalprocedure by pulling the outer sheath 30 towards the distal end of thescaffold 10 and balloon 12. This action will be described in more detaillater. It is a similar motion to the removal technique required forother coronary device products, where a single, non-constraining sheathis used to cover and protect the stent. In those cases the sheath isgrasped by the doctor or technician's gloved hands and pulled offtowards the distal end of the device. A sheath that applies a radialconstraint can be difficult to manually remove without adverselyaffecting the structural integrity of the medical device. In thesecases, it is desirable to arrange the sheaths so that special handlingis not required by the health professional when the sheath is manuallyremoved. By making the sheath removal process easy to follow orintuitive, the possibility that a health professional will damage themedical device by improperly removing the sheath is reduced.

The constraint imposed by the sheaths 20, 30 maintain the scaffold 10 atessentially the same, or close to the same diameter it had when removedfrom the crimping mechanism, i.e., the crimped crossing profile, whichis needed for traversing tortuous vessels to deliver the scaffold 10 toa target location in a body. The sheath 30 is tightly fit over thesheath 20 and scaffold 10 so that the radial inward force applied on thescaffold 10 can prevent or reduce recoil in the scaffold 10. The healthprofessional may then remove both sheaths at the time of the medicalprocedure. As such, any potential recoil in the scaffold 10 prior tousing the medical device is minimized.

The sheath 30, although imposing a tight fit on the scaffold 10 (throughsheath 30), can be easily removed by a health professional without riskof the scaffold 10 being accidentally pulled off of the balloon 12. Thisis accomplished by the manner in which the sheath 20 is positioned andremoved from the scaffold 10. If there are excessive pulling forces onthe scaffold 10 when sheaths are removed, the scaffold 10 may dislodgefrom a balloon 12, or shift on the balloon 12, thereby reducingscaffold-balloon engagement relied on to hold the scaffold 10 to theballoon 12.

When the scaffold 10 is constrained by sheath 30, as in FIG. 1, theconstraining sheath 30 is located over the section of the protectingsheath 20 where the crimped scaffold 10 is found. This sheath 30 is madefrom a polymer tube material having a thickness and pre-stressed innerdiameter size suitably chosen to cause the sheath 30 to apply a radiallyinward directed force on the scaffold 10. The thicker the tube and thesmaller the pre-stressed inner diameter size for the sheath 30 thehigher this constraint will be on the scaffold 10. However, the sheath30 thickness should not be too thick, nor its inner diameter too smallas this will make it difficult to slide the sheath 30 over, or removethe sheath 30 from the scaffold 10. If excessive force is needed toreposition the sheath 30, the scaffold 10 can dislodge from the balloon12 or become damaged when the sheath 30 is moved.

If only the single sheath 30 were used to constrain the scaffold 10,i.e., the sheath 20 is not present, the amount of preload that thesheath 30 could apply to the scaffold 10 without affectingscaffold-balloon engagement would be limited. However, by introducingthe protecting sheath 20 between the scaffold-balloon surface and sheath30 the sheath 30 can impose a higher preload on the scaffold 10 withoutrisk to the integrity of the scaffold-balloon engagement when the sheath30 is applied to and/or removed from the scaffold 10. The protectingsheath 20 therefore serves to protect the integrity of thescaffold-balloon structure as the sheath 30 is repositioned relative tothe scaffold 10.

The protecting sheath 20 extends over the entire length of the scaffold(as shown) and beyond the distal tip of the catheter assembly 2 (i.e.,the distal tip of the catheter assembly with sheaths 20, 30 removed, ascan be more easily seen in FIGS. 3B and 4C), for reasons that willbecome apparent. The protecting sheath 20 is preferably formed from aunitary piece of polymer material, which is shaped to form differentlysized portions 22, 24 and 25 for protecting the scaffold/balloon 10/12.

At the distal end 20 b of sheath 20 there is a raised end 22 in the formof a cylinder section having a larger diameter than the body portion 21of the sheath 20 to the right of end 22 which covers the scaffold 10 inFIG. 1. As such, raised end 22 provides an abutting surface with respectto distal movement of sheath 30, i.e., end 30 b of sheath 30 abuts end22 when sheath 30 is moved to the left in FIG. 1. End 22 mayalternatively take the shape of a cone with the largest diameter end ofthe cone being the most distal end of the sheath 20. The raised end 22is used to remove the sheaths 20, 30, as explained below.

The protecting sheath 20 has a cut 26, extending from the proximal end20 a to a location about at the distal the tip of the catheter assembly2. The cut 26 forms an upper and lower separable halve 28, 29 of thesheath 20. These halves 29, 28 are configured to freely move apart whenthe sheath 30 is positioned towards the distal end 20 b. The location 26a may be thought of as a living hinge 26 a about which the upper half 29and lower half 28 of the sheath 20 can rotate, or deflect away from thescaffold 10. When sheath 30 is moved distally of the scaffold 10 in FIG.1, the halves 28, 29 will tend to open up naturally, due to the preloadapplied by sheath 30 near hinge 26 a (the separable halves 28, 29 can bemore clearly seen in FIGS. 2A-2D). This arrangement for halves 29, 28allows sheath 20 it to be easily removed from the scaffold 10 withminimal disruption to scaffold-balloon structural integrity, aftersheath 30 is moved to distal end 20 b. When sheath 30 is being fittedover the scaffold 10 or removed from the scaffold 10, the presence ofthe halves 28, 29 prevent direct contact between the sliding sheath 30and the surface of the scaffold 10.

At a proximal end 20 a of sheath 20 there are portions 24 and 25 formedwhen the combined proximal ends of halves 28, 29 are brought together asin FIG. 1. When the halves 28, 29 are brought together the portions 24and 25 take the form of a stepped or notched portion 25 and a raised end24 similar to end 22, as shown in FIG. 1 and the cross-sectional view ofthe proximal end 20 a of the assembly of FIG. 1A. The notched or steppedportion 25 has an outer diameter less than the outer diameter of theportion 21 of the sheath that covers the scaffold 10, as well as theouter diameter of the scaffold/balloon 10/12. The raised end 24 has adiameter that is greater than the body portion 21. The raised end 24provides an abutment or stop 24 a preventing the proximal end 30 a ofthe sheath 30 from moving to the right in FIG. 1. As such, the end 24prevents the sheath 30 from sliding off of the scaffold 10. The portion24 also serves to identify the approximate location of the sheath 30proximal end 30 a so that it is fitted over the scaffold 10 and balloon12. Sheath 30 has a length about equal to the length of the portion 25plus the scaffold/balloon length so that when end 30 a abuts end 24 thesheath 30 will properly cover the entire scaffold/balloon 10/12 length.

Portion 25 discourages removal of the sheath 20 prior to removal ofsheath 30 from the scaffold 10. FIG. 1A shows a close-up of the proximalend 20 a from FIG. 1 with the sheath 30 (shown in phantom) replaced bythe inwardly directed preload F30 it applies to sheath portion 21 whenpositioned over the scaffold 10. A distal end of portion 25 forms aledge 25 a. When sheath 30 is positioned over the scaffold 10 theinwardly directed preload F30 applied to sheath portion 21 urges thehalves 29, 28 together. With the halves 28, 29 urged together, thescaffold/balloon proximal end 14 a blocks movement of the sheath 20 tothe left in FIG. 1A by interfering with the movement of the ledge 25 ato the left. Thus, if a user attempts to pull the sheath 20 off prior toremoving the sheath 30 from the scaffold 10 area (which can damage thescaffold/balloon integrity), there will be resistance to this movementdue to the ledges 25 a abutting the balloon proximal end 14 a (the ledge25 a thus may be thought of as an interference or interfering ledge partof the sheath 20). This resistance should indicate to the user that thesheaths 20, 30 are being removed in an improper manner. When the sheaths20, 30 are removed properly, the first sheath 30 is moved to the distalend 20 b of the sheath 20 (thereby removing the preload F30) so that thehalves 28, 29 freely open up to allow the ledge 25 a to easily pass overthe scaffold 10 so that sheath 20 is removed without resistance. Theuser is thereby informed that the sheath 20 is removed properly whenthere is no resistance to removing the sheath 20 from theballoon-catheter assembly 2.

Thus, scaffold-balloon integrity is protected by the presence of thehalves 28, 29 and the notched portion 25, as discussed above. Theextended length of sheath 20, beyond the tip of the catheter assembly 2,e.g., is about equal to a length of the scaffold 10, the length of thesheath 30 or greater than both. This length beyond the distal tipfacilitates an intuitive sliding removal or attachment of the sheath 30from/to the scaffold 10 by respectively sliding the sheath 30 along thesheath 20 extension that is beyond the distal tip of the catheterassembly 2. The length of the sheath 20 that extends beyond the distalend 4 of the catheter assembly 2 (length L21 in FIG. 4A) may depend onthe choice of sheaths used. For example, from the perspective of thehealth professional removal process, if the sheath 20 is more stiff(e.g., higher wall thickness and/or modulus) relative to the sheath 30then the length beyond distal end 4 for sheath 20 may be longer so thatthe halves 28, 29 of sheath 20 can be more safely displaced from thescaffold 10 by clearing the sheath 30 more distally of the scaffold 10.If the sheath 30 wall thickness and/or modulus is higher relative tosheath 20 than the length may be shorter since the sheath 30 will tendto naturally open up the halves 28, 29 as it is moved distally of thedistal tip of the catheter assembly 2. Also, a thicker or higher modulussheath 20 and/or sheath 30 may be desirable to increase the resistanceto improper removal of sheath 20, e.g., as when a user attempts toremove sheath 20 with, or before removing sheath 30 from the scaffold 10(as discussed earlier).

Referring to FIGS. 2B-2D, there are shown various views of the sheath20. FIG. 2A shows the sheath 20 with the sheath 30. As mentioned abovesheath 30 is sized to have a length L30 such that sheath 30 applies asufficiently uniform radial inward force or preload on the scaffold 10when end 30 a abuts end 24 a. The length L30 should therefore beslightly greater than the length of the scaffold-balloon structure. Thesheath 30 can be slid towards or away from the scaffold location (i.e.,its location in FIG. 2A or FIG. 1) over the sheath outer surface 20. Asnoted earlier, the sheath 20 has separable upper and lower halves 29, 28formed by a cut 26 made across the tube forming sheath 20. FIG. 2D is aperspective view of the upper and lower halves 28, 29 separated fromeach other. As can be appreciated from this view, the halves 28, 29rotate about the hinge 26 a when they separate. FIGS. 2B and 2C show anadditional side and perspective view, respectively, of the sheath 20showing the aforementioned structure, including the portions of notchedor stepped portion 25 and end 24 discussed earlier.

The length L20 in FIG. 2C should be chosen to extend over the scaffold10 length as well as a sufficient distance beyond the scaffold 10 sothat the sheath 30 can be pushed onto the scaffold 10, and removed fromthe scaffold 10 while the halves 28, 29 are disposed over the scaffold10. The length L20 may be at least twice the length of sheath 30, i.e.,L20=2*L30, to achieve this purpose. This length should be sufficient toallow the upper and lower halves 28, 29 to peel or rotate about theliving hinge 26 a and freely away from the scaffold surface (as in FIG.2D) without interfering with the sheath 30.

As mentioned earlier, a thicker tube and smaller inner diameter forsheath 30 will cause the sheath 30 to apply a greater pre-load on thescaffold 10. The sheath 30 thickness and/or inner diameter size isselected with the sheath 20 in mind. That is, the sizing of one candetermine what sizing to use for the other, based on achieving anappropriate balance among the amount of pre-load F30 (FIG. 1A) desired,the ease in which the sheath 30 can be placed over or removed from thescaffold 10 location, increasing resistance to improper removal ofsheath 20 (ledge 25 a abutting proximal end 14 a, as discussed above)and avoiding disruption to the integrity of the scaffold-balloonstructure, e.g., pulling the scaffold 10 off the balloon when the sheath30 is being removed. For example, if a relatively thin and/or lowmodulus tube is used for sheath 20 (as compared to sheath 30), thesheath 30 will impose a higher localized pre-load on the scaffold 10.And the scaffold 10 is more likely to be affected by sheath 30 movementbecause the sheath 20 easily deforms under the movement of the sheath30. If the sheath 20 is made thick and/or a higher modulus tube materialis used for sheath 20 (compared to sheath 30) the scaffold 10 will notbe as affected by movement of the sheath 30. And local changes inpre-load on the scaffold 10 will tend to be lower since the sheath 20does not deform as easily under the movement of the sheath 30.

Referring to FIGS. 3A-3D, methods of assembly using the sheaths 20, 30(sheath pair) are now described. The scaffold 10 is crimped to theballoon 12 of the catheter assembly 2 using a crimping mechanism. Asnoted above, for a polymer scaffold the diameter reduction duringcrimping may be 2:1, 2.5:1, 3:1, 4:1 or higher. This diameter reductionintroduces high stresses in the scaffold structure. The memory in thematerial following crimping causes recoil of the scaffold structure, asdiscussed earlier.

One can incorporate lengthy dwell times within the crimper, e.g., afterthe final crimp step, to allow stress-relaxation to occur in thestructure while heated crimper blades are maintaining a fixed diameterand temperature to facilitate stress relaxation. Both the dwell periodand the imposition of a constraining sheath over the crimped scaffoldafter crimping helps to reduce recoil after crimping. Crimping of thescaffold 10 to the balloon 12 including desirable dwell times andtemperatures that can affect stress relaxation and recoil after crimpingare disclosed in U.S. patent application Ser. No. 12/861,719 (docket no.62571.448), U.S. patent application Ser. No. 13/089,225 (docket no.62571.517) and U.S. patent application Ser. No. 13/107,666 (docket no.62571.522).

The sheath pair, shown in FIG. 3A, is placed on a mandrel 8 before beingattached to the catheter assembly 2. The mandrel 8 is passed through thecatheter shaft 4 guidewire lumen (not shown), and exits at the distalend of the catheter assembly 2. The sheath pair is then placed on themandrel 8 distally of the catheter assembly 2. The mandrel 8 is thenused to guide the sheath pair over the scaffold-balloon 10/12 asillustrated in FIGS. 3B-3D.

Referring to FIG. 3B, the distal end 30 a of the sheath 30 is adjacentto the raised end 22 of the sheath 20. In this configuration the halves28, 29 can freely open or close. The sheath pair is then brought towardsthe scaffold-balloon 10/12. The halves 28, 29 easily deflect over thescaffold-balloon 10/12. The sheath pair may be slid towards thescaffold-balloon 10/12 as follows. Holding the catheter assembly 2stationary, grasping the mandrel 8 with one hand and the sheath pairwith the other hand and sliding the sheath pair over the mandrel 8 untilthe halves 28, 29 are located over the scaffold-balloon 10/12 as shownin FIG. 3C. When properly positioned, the portions 24, 25 are positionedwith respect to proximal end 14 a as shown in FIG. 1A.

Referring to FIGS. 3C-3D, once the halves 28, 29 are located properlyover the scaffold-balloon 10/12 to protect this structure, theconstraining sheath 30 can be pushed over the scaffold-balloon 10/12 (asindicated in FIGS. 3C-3D by P). The sheath 30 may be pushed over thescaffold-balloon 10/12 in the following manner. The raised end 22 andmandrel 8 are grasped with one hand to hold the two stationary. Then,using the other hand the sheath 30 is pushed over the scaffold-balloon10/12 until the end 30 a of sheath 30 is disposed adjacent to, or abutsthe raised end 24 of the sheath 20, which indicates the proximatelocation of the proximal end 14 a of the balloon-scaffold 10/12.Alternatively, the portion 24 and catheter shaft 4 may be simultaneouslyheld with on hand, while the sheath 30 is pushed towards the scaffold 10with the other hand. By grasping the portion 24 with the catheter shaft4, the halves 28, 29 are held in place relative to the scaffold 10 whilethe sheath 30 is being pushed over the scaffold 10.

The catheter assembly 2 with sheaths arranged as in FIG. 4A is packagedand sterilized. At the time when the catheter assembly is to be used ina medical procedure the package is opened and the sheath pair removedfrom the distal end. The catheter assembly 2 is not configured for beingintroduced into the patient until the sheath pair is removed. FIGS. 1,1A and 4A depict the arrangement of the sheaths 20, 30 at the distal endof the catheter assembly 2 when the packaged and sterile medical deviceis received by a health professional. Examples of such sterile packagingis found in U.S. patent publication no. US 2008-0010947 (docket no.62571.60). The sheath 20 extends well-beyond the distal tip of thecatheter assembly 2 such that it overhangs this distal tip. Theoverhanging portion of the sheath 20, which has a length of more thanL21 (FIG. 4A), is provided to facilitate a safe and intuitive removal ofthe sheath pair by a health professional, thereby reducing the chancesthat the sheath pair are removed improperly.

Referring to FIGS. 4B-4C, methods for removing the sheath pair from thescaffold-balloon 10/12 by the health professional are now described.These illustrations refer to moving the sheath pair over the mandrel 8;however, a mandrel 8 is not necessary. The sheath pair may be safelyremoved from the catheter assembly 2 without using a mandrel 8.

A sterilized and packaged catheter assembly with sheaths 20, 30positioned as shown in 4A typically includes the stiffening mandrel 8 inthe catheter shaft 4 lumen to provide bending stiffness for shaft 4. Adistal end of the mandrel 8 has a curled end, or an extension/stop atthe distal end (not shown), which is used to manually withdraw themandrel 8 from the catheter shaft 4 lumen by pulling the mandrel 8towards the distal tip of the catheter assembly 2. In the followingexample the sheaths 20, 30 are removed. The proscribed steps preferablyalso include the act of removing the mandrel 8 from the catheter shaftlumen by, e.g., simultaneously gripping the raised end 22, sheath 30 andmandrel 8.

First, the sheath 30 is pulled away from the scaffold-balloon 10/12structure, where it is shown positioned in FIG. 4A. The sheath 30 may bewithdrawn or pulled away from the scaffold-balloon 10/12 in thefollowing manner. One hand grasps the raised end 22 and mandrel 8, tohold the two stationary, while the other hand grasps and pulls thesheath 30 towards the raised end 22. When the sheath 30 reaches theraised end 22 the halves 28, 29 should freely deflect away from thescaffold 10 surface, since a majority if not all of the cut 26 is to theleft of the sheath 30 (FIG. 4B). At this point both sheaths 20, 30 canbe simultaneously pulled away from the scaffold-balloon 10/12.

As an alternative, the sheaths 20, 30 may be removed by grasping thecatheter assembly distal portion, e.g., the catheter shaft 4, andoptionally portion 24 as well with one hand and grasping and pulling thesheath 30 distally of the catheter assembly 2 with the other hand. Oncethe sheath 30 has abutted the raised end 22 (and removing hand fromportion 24, if being gripped with shaft 4), continued pulling on thesheath 30 distally can safely remove both sheaths without risk ofdislodging the scaffold 10 from the balloon. The pulling of the sheath30 distally, while it abuts the raised end 22, causes both the sheath 20and the sheath 30 to be removed from the scaffold-balloon 10/12. Theraised end 22 therefore functions as an abutment for removing bothsheaths in a safe manner with minimal disruption to the crimpedscaffold. This final pulling away of the sheath 20 from scaffold 10 mayalso simultaneously remove the stiffening mandrel 8 from the cathetershaft 4 lumen.

As discussed earlier, the assembly of sheaths 20, 30 discourages ahealth professional from removing the sheath 20 before sheath 30 ismoved to end 22. For example, if a health professional were to pull onthe end 22 while the sheath 30 is positioned over the scaffold, theledges 25 a abutting proximal end 14 a will interfere with distalmovement of the sheath (FIG. 1A). When this resistance is felt, thisshould indicate to the health professional that the sheath 20 is beingremoved in an improper manner. If the sheath 30 is first moved to end22, then the sheath 20 can be pulled off of the catheter distal tip veryeasily since the halves 29, 28 (free of the preload F30) will easilyopen up and pass over the scaffold 10.

In an alternative embodiment of sheath 20, the raised end or stop 22 and24 may be formed by a heat shrink process. In the examples above thestops 22, 24 were preferably formed when the tubing was formed, e.g.,insert-molding the tube shape to produce the structure 22, 24 describedin FIGS. 1-2. Alternatively, a constant-diameter tube may be formed.Radially stretched polymer rings are then placed at the proximal anddistal ends 20 a, 20 b of sheath 20. Heat is then applied to thestretched rings, which causes the rings to return to about theirpre-stretched diameter. This can secure the rings to the tube. With theextra material heat shrunk over the sheath 20 at ends 20 a, 20 b, therecan be formed stops essentially the same in function and size as stops24, 22, respectively (these heat shrunk stops will hereinafter bereferred to as stops 24′, 22′). Accordingly, the heat shrunk stop 24′can prevent proximal movement of the sheath 30 (as in the case of stop24) and the heat shrunk stop 22′ can provide an abutment for removal ofthe protecting sheath 20 with the constraining sheath 30 (as in the caseof stop 22).

The sheath 20 may be constructed with heat shrunk stops 22′, 24′ asfollows. First, a tube of length L20 is formed. The tube has a constantdiameter except where the stepped down portion 25 is located. A pair ofrings having a length about the same as the length of stops 22, 24 and adiameter smaller than the portion 21 of sheath 20 are then plasticallydeformed and placed over the desired location. Heat is then applied tothe deformed rings and tube location where the rings will be attached,to cause the ring diameters to shrink back to about their originaldiameters, which was less than the diameter of portion 21, and bond tothe tube, thereby securing the stops 24′, 22′ to the sheath 20 material.Once secured, the cut 26 may be made and the halves 28, 29 becomeseparated. The half-portions of the heat shrunk stop 24′ being locatedon each of the halves 28, 29.

An alternative to the sheath pair 20, 30 is depicted in FIGS. 5 and6A-6C. According to this aspect of the disclosure, an outer constrainingsheath (sheath 50) and inner protecting sheath 40 (sheath 40) arephysically connected to each other to form a one piece sheath pair 40,50. This one piece sheath pair offers several of the constraining sheathand protecting sheath advantages discussed in connection with thesheaths 20, 30. As such, the same discussion with regards to advantagesof sheath pair 20, 30 applies to sheath pair 40, 50 unless statedotherwise.

The connection between the sheath pair 40, 50 is depicted in FIG. 6A bya hinge 45 and portion 49 a, which hinge 45 can be a living hinge. Thehinge 45 may be thought of, alternatively, as a portion of an upper half49 of the sheath 40 (similar to upper half 29 of sheath 20) connected atits proximal end to the proximal end 50 a of the sheath 50. By thisconnection to sheath 50 half 49 (or connector 49) functions as aprotecting portion of sheath 40 for the scaffold when sheath 50 isplaced over the scaffold 10, a connector connecting sheaths 40 and 50,and as a hinge for allowing sheath 40 to be inserted into sheath 50, asdepicted in FIG. 6B. Thus, a one piece sheath pair 40, 50 can functionin a similar manner as the separate sheath pair 20, 30 discussedearlier.

The outer sheath 50 length L50 (spanning from proximal end 50 a todistal end 50 b) is about the same as length L30 of sheath 30 or longerthan sheath 30 for the reasons set out below. A length L40 for sheath 40may be the same as L20, or longer. There are additional related featuresbetween sheath pair 20, 30 and sheath pair 40, 50. The constrainingsheath, i.e., sheath 50, length L50 is at least the length of thescaffold/balloon 10/12. And sheath 40 has a hinge 46 a for deflection ofupper and lower halves 48, 49 away from the scaffold 10 after the sheath50 has been withdrawn from the scaffold 10. Thus, as with sheath 20,sheath 40 includes a cut 46 to form halves 48, 49 and hinge point 46 a.

Referring to FIG. 5, the scaffold/balloon 10/12 is within both thesheaths 40, 50 when the sheath 50 preload is applied to thescaffold/balloon 10/12, which helps to maintain the crimped profile andreduce recoil, as explained earlier. Unlike the assembly of FIG. 1,however, there is no extension of sheath 40 beyond the distal end 14 bof the catheter assembly 2. Rather, the end 40 b of sheath 40 isdisposed at about the same location, or proximal of the sheath 50 distalend 50 b when in an assembled state, e.g., as a packaged medical device.FIG. 6B depicts an extension of sheath 50 such that distal end 50 b isdistal of both of the distal ends 14 b and 40 a. In a similar fashion asstop 22 of sheath 20, the extension of sheath 50 can be gripped towithdraw sheath 40 from sheath 50, as explained below, without alsogripping sheath 40.

The sheaths 40 and 50 may be formed from a single piece of tubing, ordifferent tubing that is bonded or otherwise physically connected toeach-other to form a one-piece sheath. When physically connected, ormade from a single piece of tubing, a one-piece sheath has a protectingand constraining sheath portion that are integral in the sense thatthere is a mechanical engagement between the two. When made from asingle piece of tubing the one-piece sheath may be thought of as formedfrom a unitary piece of material.

Referring to the case of a one-piece sheath made from a single piece oftubing, the sheath construction may start with tubing cut or formed tosize, as shown in FIG. 6D. The tubing has a length equal to the sum ofthe lengths, i.e., L40+L50+L45. The one end of the tube corresponds tothe distal end of the sheath 50 and the other end of the tubecorresponds to the distal end of the sheath 40. The cut 46 is made overthe length extending from the hinge 46 a to the proximal end 51 b of thesheath 50 portion. The lower halve 48 of the sheath 40 is then separatedfrom the proximal end 50 a of the sheath 50 and the portion between 51 aand 51 b removed. The portion of length L45 may be retained, in whichcase lower half 48 extends to proximal end 51 b. As mentioned earlier,the upper half 49 serves to connect the sheaths 40, 50, protect thescaffold 10 and provide a hinge 45 for articulating the sheath 40relative to sheath 50 as shown in FIGS. 6A-6B. The sheath pair 40, 50may then be placed over the scaffold-balloon 10/12 to provide theassembly illustrated in FIG. 5, which shares many of the same advantagesas the assembly of FIG. 1.

The flexibility of hinge 45 and material forming the half 49 permits thearrangement shown in FIG. 5 where it can be appreciated that half 49 isfolded over itself when both of the sheath pair 40, 50 are over thescaffold 10. Tubing that provides desired stiffness properties forapplying a preload to the scaffold 10, protecting the scaffold 10 andwith sufficient flexibility to enable the half 49 to fold over itself,or function as a hinge 45, as illustrated, is known in the art. In analternative embodiment a desired tube thickness and/or stiffness may noteasily function as a hinge 45. In this case, the half 49 may be weakenedat the desired location or region of the hinge 45.

The prior discussion regarding tube thickness, diameter and/or modulusof material with regards to removal, preload, etc. in connection withsheaths 20, 30 applies equally to the sheath pair 40, 50. For instance,sheath 40 may have a different modulus, diameter and/or thickness fromsheath 50 where the sheaths are formed from different tubing. Whensheaths 40, 50 are made from different material, and/or have a differentwall thickness or diameter the two may be joined or connected by athermal bonding of the end 49 a to sheath 50 proximal end 50 a.

With reference to FIGS. 5, 6B and 6C methods of configuring the packagedor post-crimping catheter assembly (i.e., sheaths 40, 50 placed over thedistal portion of the balloon-catheter after crimping or when beingsterilized and awaiting use by a health professional, as depicted inFIG. 5) are discussed. The scaffold/balloon 10/12 or distal end 14 b ofthe catheter assembly 2 is inserted into the sheath 40. The halves 48,49 are free to open so that the scaffold-balloon 10/12 is easilyreceived at the distal end 40 b of the sheath 40. With the distal end 14b at about, or proximal to the distal end 40 b the sheath 40 andcatheter assembly 2 are then inserted into the sheath 50. When thesheath 40 and scaffold/balloon 10/12 are received within the sheath 50,the sheath 50 applies the desired preload on the scaffold/balloon 10/12and the halves 48, 49 have come together over the scaffold/balloon10/12. This assembly may be performed while a stiffening mandrel 8extends through the guidewire lumen of the catheter shaft 4 (as was thecase for sheaths 20, 30).

In alternative embodiments the sheath 50 may be constructed to have astepped down diameter section 52 at the distal end 50 b, which section52 forms a stop (similar in form and function to the stops formed bysection 25) that can prevent the sheath 40 from extending distallybeyond the point where the stepped-down diameter begins. At the proximalend, a clamp 42 as depicted in FIG. 6C may be used to grip both thesheath 40 and sheath 50. The pressure on the shaft 4 (which preferablyhas a stiffening mandrel 8 extending there through) by the clamp 42 maybe such as to prevent both distal and proximal movement of the sheath 50relative to the sheath 40. In one example both the clamp 42 and steppeddown distal end 52 of sheath 50 are used to facilitate an intuitiveremoval process by a health professional and ensure the sheath pair 40,50 do not shift relative to each other while the packaged medical deviceawaits use.

Referring to FIGS. 5 and 6A-6C, a method of removal of the sheath pair40, 50 begins with removing the clamp 42 from the proximal end. Theclamp 42 applies a pressure force gripping the proximal ends of bothsheaths 30, 50 to the catheter shaft 4. When removed the sheaths 40, 50may then be separated from each other. The distal end 40 b of the sheath40 is proximal of the sheath 50 distal end 50 b, since the stepped downsection 52 prevents the sheath 40 from extending further distal (in thisexample, therefore, the sheath 50 has a minimum length of L30 plus theadded length for stepped down section 52 to ensure the sheath 50 coversthe entire length of the scaffold/balloon 10/12). The healthprofessional, after removing the clamp 42, grips the stepped downsection 52 (only) and pulls it distally to remove the sheath 50 from thescaffold 10. In doing so the sheath 40 will naturally remove itself aswell from the scaffold 10 since the two sheaths are connected via half49. After the sheath 50 has been sufficiently withdrawn from thescaffold 10, the halves 48, 49 will naturally open up. As the sheath 50continues to be pulled distally the connected half 49 pulls the sheath40 from the scaffold. Since the halves 48, 49 easily deflect away fromthe scaffold at this point, there is minimal disruption to thescaffold-balloon 10/12 structural integrity.

As with the embodiments discussed in connection with FIGS. 1-2,one-piece sheaths may provide an intuitive removal for a healthprofession. By providing an extension for sheath 50 and connecting thesheaths 40, 50 it can be communicated fairly easily the steps involvedfor safely removing both sheaths. First, a holding clamp is removed.Second, the extension of the constraining sheath is gripped and pulledaway from the distal end of the catheter assembly. This single motioncan safely remove both sheaths since they are connected and theprotecting sheath will not withdraw until the constraining sheath issubstantially clear of the scaffold 10. This avoids or minimizes thepotential that damaging shear forces will be applied to the surface ofthe scaffold/balloon 10/12 structure as the sheaths are being removed.

Inner surfaces of sheaths 30, 50 may have a relatively smooth surfacetypical of polymer tubes formed by a molding or extrusion process. FIGS.7A-7C, 8A-8C and 9A-9B illustrate alternative embodiments of aconstraining sheath (sheath 30′) which may be used with either the onepiece or two piece sheath embodiments described earlier. The innersurface 70 of the sheath 30′ is formed to reduce friction between it andthe protecting sheath, e.g., sheaths 20 or 40, respectively, when thesheath 30′ is placed on, or removed from the scaffold-balloon 10/12.Sheath 30′ therefore is designed so that it may be more easily slid overa protecting sheath without adversely affecting the desired preloadprovided by the same constraining sheath not having the altered innersurface; that is, a smooth surface. A constraining sheath with anon-smooth or non-cylindrical contacting surface may also be chosen as away to increase the preload over a constraining sheath that does nothave an altered surface, but without risking damage to thescaffold/balloon 10/12 when the constraining sheath is removed. Sincethe frictional forces resisting sliding are reduced by a non-smoothsurface the preload applied to the scaffold may be higher, so thatessentially the sliding resistance is the same (if the surface contactis reduced then the preload may be increased because frictionalresistance to sliding is proportional to the product of the preload andsurface-to-surface contact area).

By reducing frictional resistance to sliding motion when a constrainingsheath is placed over, or removed from a scaffold 10, thescaffold/balloon 10/12 integrity can therefore be more reliablymaintained. If frictional resistance to sliding motion of theconstraining sheath relative to a protecting sheath is high enough tocause a constraining sheath to stick to a protecting sheath, then ashear force is applied to the surface of the scaffold 10, which canresult in dislodgment of the scaffold 10 from the balloon 12 or damageto a coating on the scaffold 10. At the same time, as discussedpreviously, it is desirable to have a relatively high preload imposed bya constraining sheath to reduce recoil of the scaffold 10. Theembodiments described below in connection with FIGS. 7A-7C, 8A-8C and9A-9B help to satisfy both of these competing needs.

The description of embodiments of a reduced-friction constraining sheath30′ may refer to assemblies shown in, or described with reference toFIGS. 1 and 5. However, a friction-reducing and/or pre-load increasing(yet safely removable) constraining sheath according to the disclosureis not limited to these arrangements. In other embodiments aconstraining sheath having a reduced friction inner surface may beapplied to constrain a scaffold 10 recoil without a protecting sheathbeing used (the stiffness and preload of the constraining sheath, and/orsensitivity of the scaffold/balloon 10/12 structure to shearing forcesis a factor to consider when deciding whether a protecting sheath isneeded). It will be understood, therefore, that the embodimentsdiscussed in connection with FIGS. 7A-7C, 8A-8C and 9A-9B may bepracticed with or without a protecting sheath disposed between theconstraining sheath and scaffold/balloon 10/12.

FIG. 7A depicts a front cross-sectional view of an alternative sheathpair to that described in connection with FIG. 1 or 5, respectively. Forthese embodiments, the constraining sheath (sheath 30′) has formed onits inner surface 70 raised ridges 72 extending over the length of thesheath 30′. The raised ridges 72 contact the outer surface of theprotecting sheath 20 while the sheath pair 20, 30′ is positioned overthe scaffold/balloon 10/12. By forming the ridges 72, there is lesssurface-to-surface contact between the constraining sheath 30′ andprotecting sheath 20. Hence, there is less frictional resistance whensliding the constraining sheath 30′ over the protecting sheath 20. Thesurface-to-surface contact is reduced from the entire contacting innerand outer surfaces of the two sheaths to mostly the edges 72 a of theridges contacting the outer surface of the protecting sheath. Thepreload is thereby applied through the edge 72 a contact with the outersurface. For a sufficient number of ridges 72 formed about thecircumference of the inner surface 70 of the sheath 30′, about the samepreload can be applied to the scaffold 10 while reducing the frictionalresistance to sliding motion between the constraining and protectingsheaths. The ridges may be formed from a mold for the outer sheath30′/50′ or extruded. FIG. 7B shows a side view of the sheath 30′according to this embodiment.

FIG. 7C shows an alternative construction for a sheath 30′ having ridgesto reduce friction. Here ridges 74 are formed using embedded wires 73within the sheath 30′ which are disposed near the inner surface 70. Thewires run lengthwise over the sheath 30′ to form similar ridges toridges 72. The constraining sheath 30′ of FIG. 7C may be formed bypositioning the wires 73 within a mold forming the sheath 30′, as isknown in the art.

FIGS. 8A-8B depict other alternative embodiments for sheath 30′.According to these embodiments o-rings 76, circumferential ridges, orrings are formed over the inner surface 70, rather than length-wiseridges (FIGS. 7A-7B). The o-rings 76 may be formed by a mold as beforeand may use embedded wire rings (as was done for the sheath of FIG. 7C)to form the raised o-ring surfaces for contacting the outer surface ofthe protecting sheath.

FIGS. 9A-9B illustrate another embodiment for sheath 30′/50′. Accordingto this arrangement several nubs 78 are distributed over the innersurface 70 to form contacting surfaces 78 a for applying the preload tothe scaffold 10. As in the case of ridges 72, 74 or o-rings 76, thereduced surface-to-surface contact provided by the nubs 78 can reducefrictional resistance to sliding motion between the protecting andconstraining sheaths without reducing the desired preload on thescaffold 10.

In alternative embodiments, the outer surface of the protecting sheathmay include ridges, rings, nubs or a roughened surface, as opposed tothe inner surface of the constraining sheath.

FIGS. 10A-10D illustrates aspects of a constraining and protectingsheath assembly according to other embodiments. Referring first to FIGS.10B and 10D, the assembly includes a shell 130 forming an innerprotecting 110 portion and outer handling 115 portion. Protectingportion 110 is connected to handling portion 115 by lengthwise extendinglink 114. FIG. 10B shows a perspective view of shell 130 and FIG. 10D afrontal view. Portions 110 and 115 are generally cylindrical in shapeand have a length about equal to the length of sheath 30, i.e., lengthof L30. FIG. 10C shows a perspective view of a compression portion 120having a shape sized to fit within the space 102 between the handlingand protecting portions 115 and 110.

FIG. 10A shows an assembled view, which constrains recoil of a scaffold10 using the assembled portions 110, 115 and piece 120. As depicted inthis frontal view, the compression piece 120 is received in the space102 to apply a compressive radial load on the protecting portion 110 tothereby apply the desired preload on the scaffold/balloon 10/12. Thehandling portion 115 is used to place the shell 130 on, and remove theshell 130 from the scaffold/balloon 10/12. The handling portion 115provides a place for a medical professional to grip, or hold onto (sothat the protecting portion 110 does not move relative to the scaffold10) while the compression portion 120 is being removed. The handlingportion 115 also acts to isolate the protection portion 110 fromexternal forces.

Referring again to FIG. 10D, the protecting portion 110 is formed byhalf cylinder portions 110 a, 110 b which naturally deflect away, orspring apart from each other when the compression portion 120 is absent,as shown (compare to FIG. 10A). This facilitates safe removal of theshell 130 from, or placement of the shell 130 over the scaffold/balloon10/12. Thus, when the compression portion 120 is removed a space formedbetween the half-cylinders 110 a, 110 b is increased such that thescaffold/balloon 10/12 can be easily inserted into or removed from theprotecting portion 110 when the compression portion 120 is absent.

The handling portion 115 is also formed by two half cylinders 115 a, 115b, but it may take on another shape while providing the same function.Also, the protecting portion 115 may be a single cylindrical piece,i.e., without a split. The handling portion 115 may also be constructedso that the half cylinders 115 a, 115 b deflect away from each otherwhen the compression portion 120 is not received in the space 102between the portions 110, 115. By having the half cylinders 115 a, 115 bspring apart like the half cylinders 110 a, 110 b, the compressionportion 120 may be more easily inserted into, or removed from the space102.

The compression portion 120 is sized to bring the half cylinders 110 a,110 b together (thereby applying a preload on the scaffold 10) whencompression portion 120 is pushed into the space 102. In a preferredembodiment, referring to FIG. 10C, the compression portion 120 has anouter radius that is smaller than the handling portion 115 and onlycontacts the protecting portion 110. For example, when the compressionportion 120 is within the space 102 the handling portion 115 retains thesame shape it had prior to inserting the compression portion 120. Thereis a gap between the compression portion 120 outer surface and the innersurface of the handling portion 115. As such, the handling portion 115need not be used to provide or attain a desired preload. The compressionportion 120/protecting portion 110 may fulfill this role, while thehandling portion 115 is used handle the shell 130 when it is positionedover or removed from the scaffold 10, or to prevent inadvertent removalor sliding of the compression portion 120 over the protecting portion110. In this embodiment the compression portion 120 is made from astiffer material than 130. This allows the compression portion 120 tocompress the half cylinders 110 a and 110 b without being significantlydeformed itself. The compression portion 120 may be described as acylindrical volume of the polymer material with a cut-out to form akey-hole like space 124 for receiving the link 114 and protectingportion 110 within the cylindrical volume.

In an alternate embodiment, the compression portion 120 is made from arelatively compressible polymer, compared to portions 115, 110. Asbefore, the compression portion 120 may be described as a cylindricalvolume of the flexible polymer material with a cut-out to form akey-hole like space 124 for receiving the link 114 and protectingportion 110 within the cylindrical volume. The compressive force isgenerated by the deformation of 120 between the handling portion 115 andthe protecting portion 110. The material may be very soft, even foam ora composite soft material with a stiff core to ease insertion andremoval. The low modulus of the material ensures that compressive forceis relatively independent of the dimensions of the sheath or thescaffold.

The key-hole like space 124 forms a space with length L for receivingthe link 114, and diameter D for receiving the protecting portion 110.The diameter D is such that the half cylinders 110 a, 110 b will beforcibly brought together when the half cylinders 110 a, 110 b areplaced within the space 124. Thus, when the scaffold/balloon 10/12 isdisposed between the half cylinders 110 a, 110 b and the protectingportion 110 inserted within the space 124, the half cylinders 110 a, 110b can apply the desired preload on the scaffold 110 due to the inwardlydirected radial compression forces caused by the compression portion120. To facilitate placement of the compression portion 120 within thespace 102, its outer surface 126 and inner surface 128 may be beveledalong the proximal end. This will allow the compression portion 120 toslid along the handling portion 115 inner surface and protecting portion110 outer surface as the compression portion 120 is being inserted intothe space 102. When inserted into the space 102, the half cylinders 110a, 110 b are forced together, so that the protecting portion 110 forms acylinder enclosing the scaffold/balloon 10/12.

The compression portion 120 length is preferably longer than the lengthof shell 130, i.e., longer than length L30. This additional lengthallows a medical professional to easily grasp the compression portion120 to remove it from the space 102. Preferably, this additional lengthwould extend distal of the catheter distal end, similar to otherembodiments, and may include a knob, raised or flared end that wouldfunction in a manner similar to the raised end 22 shown in FIG. 1.

In a method of assembly, the handling portion 115 is held while thedistal end of the catheter assembly 2 is inserted between the halfcylinders 110 a, 110 b. The compression portion 120 is then pushed intothe space 102. This configures the assembly as shown in FIG. 10A. Toremove the shell 130 from the catheter assembly 2, the compressionportion 120 is first removed by pulling on the exposed portion ofcompression portion 120 while holding the handling portion 115. Whenremoved in this manner, there are near zero shear forces acting on thescaffold 10. Removing compression portion 120, thereby cause the halfcylinders 110 a, 110 b to deflect away from the scaffold/balloon 10/12surface. The shell 130 may then be removed without causing damage to thescaffold/balloon 10/12.

FIGS. 11A-11C depicts a method of removing a sheath assembly from thescaffold/balloon 10/12 according to yet another embodiment. According tothis embodiment, a protecting sheath has upper and lower halves 140, 145of a cylinder, similar to upper and lowers cylindrical halves of sheath20 or 40. However, unlike sheaths 20, 40 the halves 145, 140 are notconnected to each other and extend sufficiently proximal of the scaffold10 so that they may be gripped by a health professional and pulledradially outward to cause the constraining sheath 150 to be pushed offof the distal end of the catheter assembly. According to thisembodiment, the constraining sheath 150 is removed by pulling radiallyoutward on portions 145 a, 140 a, which portions may be regarded as atwo-piece protecting sheath. Such an embodiment may be employed toassist with removal of a single sheath by disposing the halves 140, 145over the scaffold/balloon 10/12 before the sheath 150 is placed.

FIG. 11A shows a side view of a constraining sheath 150 over thescaffold/balloon 10/12. The protecting sheath has upper and lower halves145, 140 which extend proximally of the scaffold 10. This is thearrangement of the packaged balloon-scaffold catheter assembly. Toremove the sheaths, the health professional would grip the ends 145 a,140 b of the protecting sheath and pull them radially apart from eachother, as indicated in FIG. 11B. As the ends 145 a and 140 a are pulledoutward, the constraining sheath 150 is stretched radially outward andpushed distally to cause it to fall off of the end of the catheterassembly 2, as shown in FIG. 11C.

Alternatively, the health professional may grip 150 and slide distally.Once 150 is no longer constraining, halves 140 a and 145 a will fallapart and release its constraint around the scaffold/catheter assembly10/12.

FIGS. 12A-12B depicts aspects of a one-piece sheath that both protectsand constrains a scaffold/balloon 10/12 via a braided inner sleeveportion connected to the sheath. For this embodiment a constrainingsheath 170 has an inner sleeve 160 attached to an inner surface of theconstraining sheath 170. The inner sleeve 160 functions as a protectingsleeve portion of the sheath 170 to minimize shearing forces on thescaffold/balloon 10/12 as the constraining sheath 170 is removed fromthe scaffold/balloon 10/12. The inner sleeve 160 is formed as a braidedwire sleeve. By forming the inner sleeve of braided wire, it will tendto roll outward proximally (as shown in FIG. 12B) as the constrainingsheath 170 is pulled distally to remove it from the catheter assembly 2,rather than slide or dragged along with the constraining sheath portion170 as it is pulled distally to remove the sheath 170 from thescaffold/balloon 10/12. In doing so, shearing forces on the scaffold 10are minimized.

The braided wire sleeve 160 may be secured to the proximal end 170 a ofthe constraining sheath 170 so that the sleeve 160 when removed from thesheath 170 is disposed proximally of the sheath 170. To assembly thedevice shown in FIG. 12A, the braided sleeve 160 is placed over thescaffold 10 so that the proximal end of the constraining sheath 170 isdisposed distally over the scaffold 10. Then the sheath 170 is pushedover the braided wire sleeve 160.

As discussed earlier, a preferred crimping process includes a dwellperiod following the final crimp to reduce recoil of the scaffold whenthe crimping blades are removed. According to another embodiment of aconstraining sheath a heat shrink process is utilized to affix aconstraining sheath over a scaffold 10 to reduce recoil of the scaffold10 after crimping. This heat shrink method of applying a constrainingsheath may also reduce the dwell time needed to limit recoil of ascaffold 10 after crimping.

According to a method of crimping, a crimping process at or near to aglass transition temperature of the polymer of the scaffold 10 isconducted as explained in U.S. application Ser. No. 13/089,225 (docketno. 62571.517) including FIGS. 1A and 1B and paragraphs [0042]-[0065].Following crimping a radially stretched sheath is positioned over thescaffold 10 and heat applied to cause the sheath to heat shrink over thescaffold 10. In contrast to other embodiments, the heat shrunk sheathmay provide not only a tight, constraining fit over the scaffold 10, butmay also serve to reduce the scaffold/balloon 10/12 crossing profiledown further due to the inherent inwardly directed compression forcescaused by the heat shrunk tube.

Removal of a heat shrunk sheath may be facilitated by placing tabs,e.g., tabs or halves 145, 140 as in the embodiments of FIGS. 11A-11C,between the sheath and scaffold 10 surface before heat is applied to thestretched sheath. To remove the heat shrunk sheath from the scaffold 10,the half-cylinder tabs 145, 140 may be pulled radially outward, asexplained earlier, to cause the heat shrunk sheath to be pushed off thedistal end of the catheter assembly 2 without causing damaging to thescaffold/balloon 10/12.

In alternative embodiments, a sheath may be formed with slits orweakened areas that will facilitate a tearing away of the sheath when itis attached to a scaffold via a heat shrink. Examples of sheaths withslits or weakened areas for this purpose are described in U.S.application Ser. No. 12/916,349 (docket no. 104584.7) including FIGS.5A, 5B, 6A and 6B and paragraph nos. [0053]-[0055].

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification. Rather, the scope of the invention is to bedetermined entirely by the claims, which are to be construed inaccordance with established doctrines of claim interpretation.

1-24. (canceled)
 25. An apparatus, comprising: a catheter including ascaffold having a length, the scaffold comprises a polymer and thescaffold is crimped to a balloon of the catheter; a sheath assemblydisposed over the scaffold and applying a radially inward force on thecrimped scaffold to limit recoil of the scaffold, the sheath assemblycomprising: a shell forming a cylindrical protecting portion and acylindrical handling portion, which surrounds the protecting portion,and a compression portion located within a space between the protectingportion and the handling portion.
 26. The apparatus of claim 25, whereinthe scaffold is crimped by way of plastic deformation of the scaffold tothe balloon such that when the sheath is removed the scaffold retainssubstantially the same diameter it had when disposed within the sheath;and wherein the apparatus is configured into an implantable medicaldevice only after the sheath is removed.
 27. The apparatus of claim 25,wherein the sheath assembly further comprises a link connecting theprotecting portion to the handling portion.
 28. The apparatus of claim27, wherein the scaffold has a length and the link extends over thelength.
 29. The apparatus of claim 28, wherein the compression portionincludes a space extending over a length of the compression portion, andwherein the link occupies the compression portion space.
 30. Theapparatus of claim 25, wherein the protecting portion includes a slotextending along a length of the protecting portion.
 31. The apparatus ofclaim 30, wherein the handling portion includes a slot extending along alength of the handling portion.
 32. The apparatus of claim 25, wherein alength of the compression portion is longer than a length of thehandling portion and a length of the protecting portion.
 33. Theapparatus of claim 32, wherein an end of the compression portion isflared, or includes a knob.
 34. An apparatus, comprising: a catheterincluding a scaffold having a length, the scaffold comprises a polymerand the scaffold is crimped to a balloon of the catheter; a sheathdisposed over the scaffold, the sheath comprising: a first cylindricalmember in contact with the scaffold, a second cylindrical memberapplying a radially compressive force on the first cylindrical member,and a third cylindrical member surrounding the first and secondcylindrical members.
 35. The apparatus of claim 34, wherein the sheathfurther comprises a link connecting the first and third cylindricalmembers.
 36. The apparatus of claim 35, wherein the link extends over alength of the first and third cylindrical members.
 37. The apparatus ofclaim 35, wherein the second cylindrical member is configured for beingremoved from the first cylindrical member while the third cylindricalmember remains surrounding the first cylindrical member.
 38. Theapparatus of claim 35, wherein at least one of the first and thirdcylindrical members comprise a lengthwise space or slit extending over alength of the at least one of the first and third cylindrical members,the lengthwise space or slit defining half-cylinder portions of the atleast one of the first and third cylindrical members.
 39. The apparatusof claim 35, wherein the second cylindrical member comprises a space andthe link extends through the space.
 40. An apparatus, comprising: acatheter including a scaffold having a length, the scaffold comprises apolymer and the scaffold is crimped to a balloon of the catheter; asheath disposed over the scaffold, the sheath including a handle that isgripped by a medical professional when the sheath is removed from thescaffold, the sheath comprising: a first member in contact with thescaffold, the first member having a length, a second member applying aradially compressive force on the first member, the second memberincluding a space separating half-cylinder portions of the secondmember, a link extending through the second member space and connectingthe first member to the handle, wherein the apparatus is configured intoan implantable medical device only after the sheath is removed from thescaffold.
 41. The apparatus of claim 40, wherein the sheath isconfigured for being removed from the scaffold using the followingsteps: holding the handle, thereby preventing relative movement betweenthe first member and the scaffold, while holding the handle, removingthe second member from the first member, and after removing the secondmember, removing the first member from the scaffold.
 42. The apparatusof claim 40, wherein the first member includes a space separatinghalf-cylinder portions of the first member.
 43. The apparatus of claim42, wherein the first member has a first side and a second side,opposite the first side, wherein the first member space is located onthe first side, and the second member space is distal the first side andproximal the second side.
 44. The apparatus of claim 40, wherein a gapseparates an outer surface of the second member from an inner surface ofthe handle.